Metal-semiconductor barrier devices such Schottky diode devices are widely used. For example, Schottky diodes are often integrated into digital logic circuits as fast switches. Also, discrete Schottky diodes are used as power rectifiers because, among other things, they sustain high currents at lower voltage drops compared to diffused pn-junction diodes. Additionally, Schottky diodes are used as variable capacitors that can be operated efficiently, for example, at microwave frequencies.
The integration of Schottky diodes into integrated circuits is assisted by the fact that many such circuit utilize n-type semiconductor material and aluminum contacts in their manufacture. Aluminum forms a blocking contact with n-type silicon if the n-type doping is sufficiently low enough to prevent tunneling electrons from penetrating the barrier. By way of example, doping less than about 1017 atoms/cm3 is sufficient to provide a good barrier junction. Also, the barrier height of a Schottky barrier comprised of n-type silicon and aluminum is about 0.70 electron volts (eV), and such devices approximate theoretical device characteristics under forward bias quite well.
However, because of the planar structure of typical Schottky devices used today, the breakdown voltage under reverse bias typically is lower than what is desired. This is because the concentration of electric field lines increases near corners of the devices, which detrimentally impacts the abruptness of the reverse breakdown voltage. In addition, when aluminum is used to form the Schottky barrier contact, aluminum spikes are known to form at the edges of the active region because of an interaction between the aluminum, silicon and oxygen from adjacent passivating layers. The aluminum spikes can cause localized high concentrations of electric field lines, which also degrades reverse breakdown voltage.
One technique that manufacturers have used to counteract the effects described above includes diffused guard rings. One problem with the diffused guard ring approach is that they complicate device processing, and they are not suitable for higher forward voltage devices. It is also known to use extended metal flaps overlying thick dielectric regions to enhance reverse breakdown voltages of devices. However, this approach does not solve the aluminum or metal spiking problem described above, which degrades reverse breakdown voltage.
Accordingly, a need exists for a Schottky diode structure and method of manufacture that improves reverse breakdown voltage performance, that is simple to integrate into existing integrated circuit process flows, and that is cost effective.